MathLabs

Problem 5

Determine, with proof, whether one can find 19751975 points on the circumference of a circle with unit radius such that the distance between any two of them is a rational number.
Step 5 of 5: Repeat until 1975 points are chosen
n=1975  ⟹  AB∈Q for every pair of chosen pointsn=1975\implies AB\in\mathbb Q\text{ for every pair of chosen points}
Detailed analysis

Starting with two points and applying Step 4 inductively, we can choose 1975 distinct points. Step 3 makes every pairwise chord rational. Therefore the answer is yes.